1. Field of the Invention
The present invention relates to an optical recording reproducing apparatus, and more particularly, to an optical recording reproducing apparatus and an apparatus for removing dust and contamination material attached to an optical disc.
2. Description of the Related Art
Generally, an optical recording reproducing apparatus is an apparatus for making laser beam irradiated from an optical pick-up unit be incident on an active recording layer of an optical disc, an optical recording medium, through an objective lens and thereby reproducing information recorded in the optical disc or recording information in the optical disc. The optical recording reproducing apparatus was disclosed in the application Ser. No. ‘5,661,711’ registered in the U.S.A patent with a date of Aug. 26, 1997.
The optical recording medium or a magneto-optical recording medium can have high density recording capacity when a pit size is small and a track width is narrow. However, a structure of the recording medium including a protective layer, an active recording layer, and a reflective layer, a condensing method according to that, diffraction of a spot size of light collected on the recording medium in order to form a pit on the active recording layer of the recording medium are limited. According to this, an optical recording reproducing method has been actively researched.
Hereinafter, a conventional optical recording reproducing method using a far-field method will be explained with reference to FIG. 1. FIG. 1 shows an objective lens and an optical disc for explaining the conventional optical recording reproducing method using a far-field method.
As shown in FIG. 1, in the conventional optical recording reproducing method using a far field, laser beam irradiated from an optical pick-up unit (not shown) is concentrated into an optical disc through an objective lens 11 having a numerical aperture NA of approximately 0.5˜0.6. Herein, the concentrated laser beam transmits a transparent substrate 12 of the optical disc and then is made to be incident on an active recording layer 13 of the optical disc. That is, in order to prevent the active recording layer 13 from being damaged due to the user's fingerprint, dust, and contamination material, the thick transparent substrate 12 is formed on the active recording layer 13 of the optical disc.
A recording density of the optical disc is determined by a size of the concentrated laser beam, and the size of the laser beam is determined by wavelength λ of light source and the numerical aperture NA of the objective lens.
Therefore, in the conventional optical recording reproducing method using a far field method, a lens having a high refraction index, that is, high NA can not be used since the laser beam reaches to the active recording layer 13 by transmitting the thick transparent substrate 12.
Also, in order to form a focal point of the laser beam concentrated through the objective lens 11 on the active recording layer 13, the objective lens 11 and the active recording layer 13 have to maintain a constant distance. However, since a surface of the transparent substrate 12 is not generally smooth, it is impossible that the objective lens 11 contacts to the surface of the transparent substrate, the surface of the optical disc, thus records and reproduce a signal. According to this, a predetermined interval is necessary between the objective lens 11 and the optical disc, and a lens having high NA can not be used.
In order to solve said problems of the conventional optical recording reproducing method using a far field, recently, an optical recording reproducing method using a near field has been proposed as a method for enhancing a recording density in a region where diffraction of light is not generated.
A principle of the optical recording reproducing method using a near field will be explained as follows.
Incident light into a lens with a degree of an angle more than a critical angle is totally reflected when it progresses from glass having a high refraction index to air having a low refraction index. At this time, light having a very weak intensity is on a surface of the lens by the total reflection of light, which is called as evanescent wave. By using the evanescent wave, high resolution which was impossible in the conventional far field due to diffraction of light is possible. In the optical recording and reproducing optical system using the near field, light is totally reflected in the lens thus to generate the evanescent wave on the surface of the lens, and information is recorded and reproduced by coupling between the evanescent wave and the recording medium.
FIG. 2 shows a construction of the optical recording reproducing apparatus using the near field in accordance with the conventional art in order to explain an optical recording reproducing method using the near field.
As shown in FIG. 2, in the optical recording reproducing method using the near field, laser beam irradiated from the optical pick up unit (not shown) is focalized on an objective lens 22 having high NA through a slider 25 where the objective lens 22 is mounted, and evanescent wave generated from the focal point and an active recording layer 23 formed on the surface of the optical disc are coupled thus to record or reproduce information.
Therefore, in the optical recording reproducing method using the near field, the objective lens 22 having very high NA has to be used, the active recording layer has to be formed on the surface of the optical disc in order to form the focal point of the lens on the active recording layer 23 of the optical disc, and an interval between the objective lens and the optical disc surface has to be tens of nm which is less than wavelength of light.
According to this, a space for forming a passivation layer (for example, a transparent substrate) on an outer surface of the active recording layer 23 of the optical disc was not enough.
In the meantime, the objective lens 22 reciprocates the optical disc rotated in a high speed with a very near interval corresponding to tens of nm in order to scan a track of the optical disc. Also, laser beam is focalized on the active recording layer of the optical disc when information is recorded in the optical disc, which causes temperature of the surface of the optical disc to be increased.
According to an experimental result, temperature of the active recording layer is increased up to 200˜250° C. in case of a magneto-optical disc, and increased up to 600° C. in case of a disc of a phase change method. At this time, temperature of the surface of the optical disc formed by a dielectric layer and a protective layer which protect the active recording layer is also increased up to 60˜300° C., so that a following problem is generated on the surface of the objective lens adjacent to the surface of the optical disc.
That is, material constituting the optical disc and contamination material attached to the surface of the optical disc are transferred to the surface of the objective lens and a lower surface of the slider and coated by high heat of the surface of the optical disc. Herein, the contamination material includes transparent substrate material of the optical disc, hub material, cartridge material, material for constituting the surface of the optical disc such as a lubrication layer and a protective layer, material for constituting a man's fingerprint, dust, and etc. As a result of an analysis, the contamination material included carbon and fluorine compound mainly and sodium, silicone compound, and etc. were also detected.
Also, when information of the optical disc is continuously reproduced or information is continuously recorded in the optical disc, the contamination material attached to the surface of the optical disc is transferred to the surface of the objective lens and coated on the surface of the objective lens and on the lower surface of the slider by heat thus to decrease transmissivity of the objective lens. Besides, if the contamination material is coated on the surface of the objective lens for a long time, information can not be recorded in the optical disc and information recorded in the optical disc can not be reproduced.